


Attack on Gravity Falls

by AmaranthPrincess21



Category: Gravity Falls, Shingeki no Kyojin | Attack on Titan
Genre: Crossover, F/M, Miniseries, other stuff will happen too, there'll be a focus on rivetra but it won't be just a rivetra fic
Language: English
Status: Completed
Published: 2015-03-18
Updated: 2015-05-17
Packaged: 2018-03-18 10:18:26
Rating: Teen And Up Audiences
Warnings: Graphic Depictions Of Violence
Chapters: 4
Words: 10,141
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/3566012
Author URL: https://archiveofourown.org/users/AmaranthPrincess21/pseuds/AmaranthPrincess21
Summary: <blockquote class="userstuff">
              <p>After exploring a bridge between their world and the town of Gravity Falls, Petra and Levi get trapped in the strange Oregon town after their portal vanishes. With the help of Dipper and Mabel, they must find a way back home. But when titans start appearing in Gravity Falls, it's apparent that getting home isn't the only thing Levi and Petra need to worry about.</p>
            </blockquote>





	1. Chapter 1

The forest was as quiet as a grave as Levi made his way through the tall trees. It was a dangerous trek but no path had been made to the secret base just yet. There were plans in place but it would be months before it started. After all, it’d taken a very long time for base itself to be made. It was small, no bigger than a barn, but it had large walls and a spiked roof to keep the titans out; because it was right outside Wall Maria, it was a necessity. Building something in titan territory was no easy feat but if Hange’s assumptions were correct, this base and it’s biggest secret could end up being the savior of humanity. 

No titans seemed to be in the area and Levi dropped to the ground into the walled but open air entry courtyard before banging on the thick metal door of the base.

“It’s Levi,” he yelled and the door opened instantaneously. He slipped in and the door was bolted shut again. Hange, Erwin, and Mike stood in the small room. All of them were huddled around the shimmering circle in the ground, taking notes as Nifa dropped various objects into the circle. As soon as the object hit the shimmering material it vanished. 

“Have we gotten any of that shit back?” he asked Petra. She was standing near the door, leaning against it and an uneasy look on her face. 

“No. We’ve gotten some odd things from . . . from whatever that is. We got some kind of weird flatbread sandwich with weird things inside it, a cat managed to get up, and we got a ball of yarn, but we haven’t gotten back anything we’ve put down there,” she informed him. 

“We think it’s a portal of some kind, but we don’t know where it leads, if anywhere,” Hange said loudly so Levi could hear her. 

“Well, obviously it has to lead somewhere. Otherwise we wouldn’t get anything back from it,” he pointed out.

“That’s what we’re thinking, but really there isn’t any way to confirm nor deny that hypothesis,” Hange replied. 

“Have we considered sending anyone down there to see where it leads?” Levi asked. Beside him, Petra tensed up. It didn’t take a genius to figure out she was uncomfortable with his suggestion. If it wasn’t a serious question, he’d feel bad about asking it.

“No, we haven’t,” Erwin said, frowning. “We don’t know if it’d be safe.” 

“You said a cat managed to get through the portal. That means something living can go through the portal and live,” Levi said. “I’ll go down this thing and see what’s on the other side.”

“I’ll go with you, Captain!” Levi sharply turned to Petra, who had that stubborn look of determination on her face.

“No. I’m doing this alone. I’m not putting any of my subordinates in danger,” Levi told her. He fully well knew why she was so concerned. Levi was well aware of the small crush Petra had on him and if he was being honest with himself, he didn’t want her to join him because he didn’t want to put her life at risk. He wouldn’t know what to do with himself if he lost her.  

“With all due respect sir, you pointed out that things can go through the portal and live, and although I know you’re capable, you need back-up just in case something happens,” she said. 

“She does have a point, Levi, but I’m reluctant to let either of you down there,” Hange admitted, peering down into the shimmering void. “We don’t know what will happen.”

“There’s only one way to find out. Levi and Petra are capable soldiers and I trust in them to figure this out,” Erwin spoke up, blue eyes shifting over to the two soldiers. “Anchor your gear’s hooks and go down there. If anything happens, Mike and I will pull you back up.” Levi gritted his teeth but nodded. There was no arguing in this situation; he could tell by the look in Erwin’s eyes that if he tried to argue, it would be a battle he couldn’t win. He sank his hooks into the stone wall of of the base and stood at the edge of the portal. Sick anticipation boiled over in his stomach and part of him wondered if this would be his final moments.  _No, we know things can live when they go through the portal. Petra and I will be fine._ His silver-blue eyes slid over to watch her anchor her hooks. She turned to him, a look of fierce determination written on her face.

“Are you ready, Captain?” she asked.

“I’m ready, Petra,” he replied. He looked to Erwin, who nodded. Levi crouched down and slowly entered the shimmering void, hanging onto the edge before engaging his gear and slowly lowering himself down. He glanced over to Petra. She looked like the was doing just fine, maybe doing even better as she was far lower down the portal than he was. “How are you doing, Petra?” he asked, his voice bouncing around and echoing.

“I’m fine, sir,” she called back up to him. 

“Erwin, can you hear us?” Levi yelled. No response. “Shit, how are they going to know if something happens?”

“I don’t know. I guess we just hope for the best,” she replied. She paused, waiting for Levi to catch up to her and together they descended down the blank void. Rays of colors ripped through the void as they went deeper and deeper.

“When are we going to reach the bottom of this?” he wondered aloud.

“We’ve got to get there eventually. There has to be something on the other end,” she said. As they went deeper and deeper the walls around them became more and more colorful. Levi hoped that meant they were getting closer to the end. The colors were moving around at a rapid rate and flying in front of them like birds of prey and before Levi could do anything everything was shaking.

“Shit, Petra, we have to get out of here,” he said, pressing on his gear’s triggers to send him back up to the base. He and Petra only made it a few feet before their hooks came hurtling down towards them. It felt like he was in water, floating and weightless until gravity kicked it and he and Petra hurtled down the rest of the portal. No matter how many times he pressed on the triggers of his gear it refused to work. “Petra, is your gear working?!” he yelled to her.

“No, sir! It’s not!” she yelled back.  _Fuck, we’re going to die and it’s all my fault,_ Levi thought, gritting his teeth.  _She’s going to die and it’s entirely my fault for letting her come with me._ The colors swirling around them faded to white and before Levi could fully register what was going on, their world seemed to flip and instead of falling they were ascending. The white void they had been trapped in vanished and it looked like they were in a forest. Levi heard shouting but couldn’t make out the words with all the wind rushing around his ears. He and Petra fell to the grassy forest floor with a soft  thump.

“Whoa, Dipper, look! People came through the -”

“Yeah, I see them, Mabel.” Levi looked up to see a pair of twins standing in front of them, looking at him and Petra curiously. 

“Are you guys okay?” the girl asked, extending her hand out to Petra. She gladly took it and stood up while Levi got up by himself. He looked back to check on the portal only to find it gone, a patch of luscious grass where it once sat.

“Yeah, we’re fine. Where are we, though? Are we still outside Wall Maria?”

“Wall what?” the boy asked, raising an eyebrow. “We’re in Gravity Falls, Oregon. Where did you guys come from? We’ve been getting stuff from that portal for a few months now. What’s on the other side?”

“Our home,” Petra replied. “We found the portal after coming home from an expedition and we cordoned the area off.” She cleared her throat and extended her hand to the boy. “I’m Petra, and this is Captain Levi.”

“Captain? Does that mean you have a ship?” the girl inquired excitedly. “Can we go home with you and ride on your ship? Ooh! Are you a pirate?”

“What? No, I’m not that kind of Captain,” Levi said dismissively. 

“So you’re a military captain?” the boy asked. Levi nodded. “That’s pretty cool. I’m Dipper and this is my sister Mabel,” he said, gesturing to himself and his sister. 

“It’s nice to meet you,” Petra replied pleasantly. “We, um, we don’t mean to leave all of a sudden, but we really need to get back home. Do you know if this portal will open back up?”

“We’ve been having them crop up all over town for a few months, but this one seemed like it was the only permanent one,” Dipper commented.  _At least there’s a chance we can get back,_ Levi thought.  _This isn’t ideal but it’s something._

“In the meantime, you can back to the Mystery Shack with us,” Mabel offered. “You guys look like you could use something to eat.” 

“We’d love to,” Petra replied before Levi could stop her. Mabel’s face lit up.

“Come on, let’s go! You guys will love the Mystery Shack!” 

  
The Mystery Shack was definitely bigger than Levi was expecting but more bizarre than he imagined. It was a dirty place full of fake curiosities. If he hadn’t lived in the Underground, Levi would have been astounded that someone was able to raise well-adjusted kids in such filth. But the twins were kind and got them some snacks while they went off to talk to their “grunkle.” Hell, Mabel even made them tea and it wasn’t half bad. It certainly wasn’t as good as Petra’s but it was a good cup of tea.

“Look, Petra, we need to get back to base as soon as possible,” Levi said quietly, looking up from his tea. “I don’t know how we’re going to get home other than finding another portal. Those brats seem like they know a lot about this town. I don’t want to ask for their help but I don’t see any other option.”

“I agree, sir. I think Dipper and Mabel are our best shot at getting out of here. Although, I don’t think I’d mind living in a place where food isn’t scarce,” she added, taking another cookie out of the bag. “Who wouldn’t want to live in a place where having two full pantries is the norm?” 

“Neither would I but we don’t belong here. We don’t know anything about this world and we sure as hell don’t belong here. We need to get back to the secret base and we need to get back soon,” Levi said, voice falling silent as Dipper and Mabel walked back into the kitchen. 

“What do you want first, bad news or good news?” Mabel asked, climbing onto the chair next to Levi.

“Bad news,” Levi replied.  Might as well get the worst out of the way.

“Bad news, we talked to Grunkle Stan and he says he doesn’t have room for two more people,” Dipper said, grabbing a chair and sitting next to Petra. “Good news, we found a place for you to stay until you guys can get back home.”

“More bad news, it’s that abandoned cabin where that guy killed his whole family,” Mabel said. “But I’m sure the ghosts won’t hurt you!”

“You shouldn’t have a ghost problem,” Dipper added hurriedly, as if trying to reassure the two soldiers. “We did an exorcism a week ago and it turned out fine, so you guys are safe.” Petra gave a nervous laugh and Levi flat out couldn’t tell if Dipper was joking or not.

“It’s not ideal, but we’ll take it,” Petra said. “We really appreciate your help, you two.”

“Hey, anything for a couple of tourists,” Mabel said, grinning and nudging Levi with her elbow. He gave her a dark look. 

“All right then, ignoring the awkward silence,” Dipper said, taking a cookie out of the bag. “We can lead you guys there and help you clean it up a bit.” “I think we can manage the cleaning but we appreciate the offer,” Petra replied, standing up and glancing at Levi. “We should probably get going. Levi and I have a lot to talk about tonight.” 

  
The cabin wasn’t nearly as rundown as Levi or Petra imagined. In fact, it was in pretty decent shape. Everything looked old but relatively safe and intact. Mabel opened the door and ushered the two inside. 

“Here’s your new home, you two lovebirds,” she said, winking at them.

“Oh, no! We’re not dating!” Petra exclaimed.

“Sure, whatever you say,” Mabel said with another wink. “I know it’s dark in here, but there are some candles in the basement that you can use when it’s dark out.” 

“You could try turning the electricity on, but it’s probably shut off,” Dipper said.

“Turning the what on?” Petra asked.

“The electricity. You know, it’s a power source,” Mabel said, looking curiously from Petra to Levi. “Don’t you have electricity back home?”

“No, we don’t. We honestly don’t have much food back home either. Just enough to get by,” Petra admitted.

“But you two get enough to eat, right?” Mabel asked gently. The look on her face tugged at Levi’s heartstrings; he hadn’t seen someone look so distraught before over a slight food shortage.

“Well, we do, but we’re soldiers,” he replied. 

“Then maybe it’s a good thing you got sent here,” she said. “Here you won’t -”

“No,” he interrupted. “Petra and I aren’t staying. We need to get back home as soon as possible.’ He glanced over to Petra. “Come on, we’ve got a lot of work to do to make this place -” The house rattled as the ground shook in an all too familiar way. Levi and Petra bolted out the front door, anxiety growing in their stomachs as they looked around. It didn’t take long for their fears to be confirmed.

In front of them stood a titan.


	2. Chapter 2

“Shit! Stay back, you two!” Levi barked at Dipper and Mabel, attaching blades to his hilts. “Petra, go for the legs and I’ll take it down!”

“Got it, sir!” she replied. Petra’s hooks anchored themselves in the titan’s thighs and she flew through the air, blades at the ready. Scarlet blood splattered everywhere as her blades sliced through the titan’s knees with precision and as it fell Levi sprang into action. The wind whipped through his hair as he soared towards the titan’s nape. And as he had done dozens of times before, he spun and cut through the nape in seconds. 

The body fell to the ground, shaking the earth as Levi landed. 

“Whoa, is the blood evaporating?” Dipper asked, grabbing Petra’s cloak and inspecting the vanishing blood.

“Yes, it is. For some reason titan blood does that. We don’t know why,” she told him. 

“That was so cool!” Mabel piped up. “You guys were like  ‘wahhhhh,’ and the titan was like ‘oh no, noooo!’” Petra laughed, looking at Mabel with a soft fondness. 

“I guess that sums up fighting titans well,” she replied before glancing over at Levi. 

“I’m more concerned with where it came from,” he said, walking over to the slowly dissipating body.  _This doesn’t make any sense. Are titans finding these portals and getting through them,_ he wondered. The heavy sound of footsteps against the grassy forest floor thudded through the air. Levi looked up and saw an older man running towards them, an almost frantic look in his eyes.

“Kids, are you all right?!” the man demanded, bending over as he caught his breath.

“Grunkle Stan, what’re you doing here?” Mabel asked, cocking an eyebrow at him.

“I heard weird noises out where you guys were and wanted to see what was up,” he explained, eyes sliding to the titan. “Hot Belgian waffles, what  _is_ that thing?!”

“It’s a creature called a titan, sir,” Petra told him. “They’re very dangerous and will eat humans if they see them. Captain Levi and I,” she gestured to herself and him. “We know how to kill them and we got this one before it managed to do any damage. They evaporate after death so you don’t have to worry about getting rid of the corpse”

“Why in the world would you kill these things?!” Grunkle Stan demanded, gesturing to the dead titan. “You could capture one of these, show it off, and make a fortune!”

“Sir, that’s . . .  that’s not a very good plan,” Petra said, trying to let him down gently.

“What do you mean, ‘not a very good plan?’” Levi demanded, eyes narrowing at both Grunkle Stan and Petra. “Look sir, trying to capture a titan and make money from it is the shittiest plan ever.” He ignored Dipper and Mabel’s wincing and kept going. “Titans will eat anybody in their path and if it got free, it would mean very bad things for Gravity Falls.”

“I appreciate your opinion, but I think the pros outweigh the cons,” Stan said. Levi gritted his teeth.

“I’ve seen the bloodbaths titans have caused and it’s the worst thing you can ever see. You’d have to be the worst kind of greedy bastard to try and make money off of something that’s killed hundreds if not thousands of people,” Levi sneered.

“Grunkle Stan, you have to admit, that whole scheme sounds really dangerous , ” Mabel pointed out, pulling on her relative’s sleeve. Grunkle Stan sighed, pinching the bridge of his nose.

“All right, all right, I’ll drop it, he acquiesced. “Anyway, I’m just glad you two are safe. I need you to come back to the Mystery Shack with me, your shifts are about to start.” The twins groaned.

“Okay, Grunkle Stan. We’ll come over later and we’ll figure out what’s going on with these portals,” Mabel said. The twins waved goodbye to the two soldiers and trudged back to the Mystery Shack. Grunkle Stan turned to Levi and Petra, holding out his hand.

“Thanks for saving the kids. They get caught up in things they shouldn’t sometimes,” he said as he shook their hands. “I’m their great uncle Stan Pines.”

“I’m Petra Ral and this is Levi,” Petra introduced herself and her comrade. 

“Are you two new in town? I don’t think I’ve seen you before,” he asked.

“Yeah, we just moved here from a town called Trost,” Levi lied.

“Is that on the coast?” Stan asked.

“Yeah,” Petra replied. “We literally just moved here yesterday so we’re still getting used to everything here in Gravity Falls.”

“Well I hope you two enjoy it here,” Stan said, giving them a short wave goodbye and following after his niece and nephew. 

“He seems fairly capable of taking care of them,” Petra noted as she and Levi went back to their cabin.

“Judging from his house and him I’d beg to differ, but it’s not like we can adopt them or something,” Levi said. “Let’s just go have dinner and wait for Dipper and Mabel to come over so we can figure out what the hell’s going on here.”

  
  


“I found some berries in the forest and I managed to shoot a squirrel for dinner,” Petra announced as she walked into the cabin. It was dark outside as she came back with her bounty. Dipper and Mabel had left hours ago, leaving Levi with a map so he and Dipper could work on finding a pattern between all of the portals’ locations. 

“Thank you, Petra. Put it on the kitchen counter and I’ll make dinner,” he told her. She didn’t move from her spot, only giving him quizzical looks. “What? I just cleaned the counter, it’s okay to put stuff on it.”

“Sir, do you even know how to cook?” she asked.

“I know enough to make us something that doesn’t taste shitty,” he replied. 

“I wouldn’t mind making dinner,” she told him, putting the food on the table. 

“No, I’m making us dinner,” he said stubbornly, getting up and abandoning the map he was working with. “How about you go over to the Mystery Shack and get Dipper and Mabel? I think I may have found where the next portal will show up.” 

“Or you could go over there and explain it to them while I fix us dinner. Why do you want to cook so badly, Captain? I don’t have you down as a person who likes cooking.” He fought back an irritated sigh.  _God, this woman’s stubborn,_ he thought.

“I don’t like cooking but that’s not -”

“Then just let me take care of it for -”

“Petra, just go get the twins!” he snapped. “I’m making us dinner and that’s final.” She sighed and walked over to him, concern in her brown eyes.

“Is everything okay, sir? You seem really tense,” she said.

“I’m fine. Just please listen to me.”

“I am listening but you seem really stressed out. I’ll go get Dipper and Mabel, but I want you to let me cook dinner while you talk to them about the next portal, okay?”

“No.”

“Why won’t you let me cook?” Her lack of patience was getting more and more evident but God, he could tell she was trying to stay calm and not lash out. 

“It’s my fault we’re here,” he admitted, looking back down at his map. “It was my suggestion and I shouldn’t have let you come with me. You’re my subordinate, Petra, and I need to look after you.”

“With all due respect, sir, we aren’t in a regular combat zone,” she said, sitting down next to him. “You’re still my superior and I respect that, but I can’t let you do everything on your own. This isn’t a one way street. And this may have been your idea, but I made the decision to go down the portal with you. It’s partially my fault. You shouldn’t blame yourself for everything.” He knew she had a point. About everything. But he needed to protect and take care of her. He felt it deep in his bones and despite the fact he wanted to act on that, he knew she was right and he had to back up a little.

“All right, Petra. I’ll let you cook dinner. I’m going to go over to the Mystery Shack and talk to Dipper and Mabel -” He didn’t have time to finish his sentence. The door to their cabin swung open and the twins walked in, Dipper’s map carefully held under his arm and Mabel lugging around a huge canvas bag. 

“We’ve made a breakthrough!” Mabel announced, dumping her bag next to the door. Dipper went over to the kitchen table and spread his marked-up map there. He made a disgusted face at the dead squirrel.

“I just came back from a hunting trip,” Petra admitted with a nervous grin, picking up the dead animal and moving it to the kitchen counter. “Do you two want to stay for dinner?”

“No thanks, we’re going out with our friends to the new pizza place in town,” Mabel said as Levi walked over to the table and sat down.

“So I was studying the map and I think I found a pattern,” Dipper said, fingers tracing dark red lines on his map. “It looks like they’re on a diagonal grid, almost. Every portal is the same distance away from an older one and they all seem to be happening in the forest.”

“We have five places where the next portal could pop up,” Mabel pointed out. “We’re still trying to figure out where exactly the next one will be, but we haven’t figured it out.”

“You don’t know in what order they’ve been popping up in?” Levi asked.

“No. It just looks like it’s been at random,” Dipper said.

“We’re just going to have to stake out those areas then,” Petra replied. 

“We can’t do that. We can’t have one person at each location. We don’t have five people in our team and the kids can’t kill titans,” Levi pointed out. “We’re better off trying to narrow it down until we find the next location.”

“If you taught us how to kill titans, Dipper and I will be fine,” Mabel said. Levi sighed, pinching the bridge of his nose. What was with him and having such determined girls in his life? 

“It’s not that simple, Mabel. It’s a dangerous task and I’ll be damned if I put you two in the line of danger,” he told her.

“Captain, they’re going to be dealing with titans anyway. Maybe we should teach them how to at  least wield the blades. Otherwise they’re completely dependent on us and we can’t guarantee safety,” Petra pointed out. Levi gritted his teeth, but nodded.

“You have a point, Petra. We’re not teaching you how to use the gear,” Levi said, looking at the twins. “I can’t easily teach you and either way, we don’t have legitimate gear for you to use. But we’ll teach you how to use our blades.”

“Cool!” Mabel piped up, a bright smile on her face. 

“Are you sure that’s safe? I mean, it looks fun and I want to learn it, but we’re twelve,” Dipper said.

“Twelve is the minimum age requirement for our military,” Levi told them, watching shock surface on their faces. “Most kids enter the military when they’re your age and start learning how to kill titans. Well, in theory. I actually didn’t go through basic training like everyone else, but I’m guessing that’s what you learn,” he added, glancing at Petra.

“I didn’t actually learn a lot of titan killing techniques until I joined the Corps. You learn a little bit of it during basics but since most recruits go to the Military Police or the Garrison rather than our branch that actually kills titans, they don’t really go over it,” she explained. 

“How do you guys even protect yourselves against titans?” Dipper asked. “What exactly is going on wherever you guys are from.” Levi chuckled and shook his head.

“That’ll take us hours to explain,” he said.

“We have time!” Mabel exclaimed, pulling up a chair and sitting next to Levi. “If you guys tell us about your home, we’ll tell you more about ours!” Levi glanced over at Petra. She nodded at him as if to say, “Tell them.” 

“All right. Gather around, brats. This is where Petra and I are from.”

  
  


“Man, that’s super messed up,” Dipper said as Levi finished explaining everything to the two. “I’m kinda glad you guys are here. It’s probably a lot safer.”

“And not mention just all around better,” Mabel commented. “I can’t believe you guys have to live like that.” 

“It’s home,” Levi said sardonically. Petra walked over to the table, two plates of food in her arms.

“Are you sure you don’t want any,” Petra asked the twins again. 

“No thanks. I like squirrels but I don’t think I’d like eating them,” Mabel said, giving Levi’s roasted squirrel a sad look. 

“And we should probably be getting back to the Mystery Shack. Our friends are probably picking us up soon,” Dipper said, pushing his chair back and rolling his map back up.

“Wait! I have something to do before we leave!” Mabel ran over to her bag and hauled it over to the table. “I figured you guys probably don’t have any extra clothes so I made you two sweaters!” 

“Mabel, you shouldn’t have!” Petra said sweetly, taking the garment from Mabel. Levi grabbed his from the twelve-year-old. The yarn was soft and and even softer grey color. She’d managed to knit the Wings of Freedom into the front.  _She’s got a good memory,_ he thought.  _She couldn’t have seen it for more than a few minutes._ “Thank you so much, Mabel!”

“Yeah, thanks,” Levi added.

“It was no trouble!” Mabel beamed. “I also brought you guys a few of those huge bottles of water, just in case!”

“Levi and I really appreciate this,” Petra told her, giving her a hug. 

“Don’t worry about!”

“We’ll be back sometime tomorrow to try and find the next portal,” Dipper said, heading towards the door. “Night, guys.”

“Good night, you two. Have fun out with your friends,” Petra said. The twins left, shutting the door behind them and leaving Levi and Petra all alone. “Is is bad that I wish they could come back home with us?”

“Only a little,” he replied with a smirk. “If you’re done with dinner, I’ll do the dishes.”

“Are you sure, Captain?” she asked.

“Yeah. And Levi. Just call me Levi while we’re here. It feels weird for you to keep calling me Captain in this place. No idea why though,” he commented, grabbing her plate. 

“I, all right, Levi,” she said, his name sounding odd but pleasant from her mouth. “I know it’s early but I think I’m going to go to bed.”

“All right. Good night, Petra,” he said.

“Good night, Levi.” She left the dining room and sauntered into the bedroom. Levi stayed up for a few more hours, cleaning and trying to take his mind off of their situation. _How the hell are we going to get home if we miss our chances,_ he wondered, scrubbing down the kitchen table. _Living here wouldn’t be so bad. Petra and I have each other and we’re relatively safe here, but humanity needs us. We’re soldiers and we need to go back home and help humanity fight back._ He put away his cleaning supplies and quietly entered the bedroom.

Petra was snug under the covers, lying on one side of the bed. _Damn it, I should’ve known,_ he kicked himself as he glared at the sole bed in the room. _I guess I’ll just go sleep on the couch._

“Levi?” Petra slowly sat up, yawning as she looked at him with sleep-filled eyes. 

“Sorry, I didn’t realize there was only one bed,” he muttered. “I’m just going to sleep in the living room.”

“You don’t have to. I don’t mind sharing a bed,” she told him. He wouldn’t either; in fact, he’d really enjoy that. But his responsible side kicked in, scolding him for considering inappropriate things with one of his subordinates.  _Do the rules even apply here,_ he wondered, letting himself inside the room and shutting the door behind him.  _We’re not back home and it’s not like either of us will get in trouble for this. It’s only for a few nights. It’s nothing._

Petra fell back asleep quickly, curled up in the blankets as Levi slowly stripped. Sleeping in his uniform wasn’t new to him, but he always fell asleep at a desk, or on his couch. He didn’t want to dirty the sheets with his uniform. He pulled on the sweater Mabel had made for him and slipped into bed. As soon as his head hit the pillow, he fell asleep.

  
  


“CAPTAIN LEVI! PETRA! GET UP! SOMETHING HORRIBLE’S HAPPENED!” Levi shot straight up out of bed at the sound of Mabel’s shrill voice. He quickly pulled a pair of pants on and ran into the living room. Petra scrambled after him, a pants and the sweater Mabel made for her hastily thrown on. Levi had seen some freaked out kids before, but the devastated and horrified looks on Mabel and Dipper’s faces was highly unsettling. 

“A portal must’ve opened last night,” Dipper informed them. “We didn’t find the portal and we think it’s closed, but we found a lot of broken trees and stuff.”

“Is anyone hurt?” Levi demanded. 

“Not that we know of,” Mabel replied. “But . . . But Grunkle Stan . . . we don’t know how he did it, but he managed to capture and keep down one of those titans.”

_“What?!”_ Levi and Petra squeaked. 

“We woke up and he had it chained down and he was building like a shed around it,” Mabel said, hurrying over to Levi and pulling on his arm. “Come on, we need to do something!”

“Hold on, we need to get our gear and then we’ll head over to the Mystery Shack,” Levi said, gently prying Mabel’s fingers off his wrist. She let go and let him and Petra hurry back to their bedroom.

“How in the hell did he managed to capture one?” Petra wondered as she got her harness on. 

“I don’t know, but we have to get him away from it and kill it before it has the chance to get free,” Levi said, getting his gear all in order.  _Shit, this just keeps getting worse and worse,_ he thought.  _If Stan can capture titans and more get through the portals, we’re going to have a huge problem on our hands. We need to kill this titan and keep this town safe._


	3. Chapter 3

“Ugh, kids, why’d you have to bring  _them_ here?” Stan groaned as the four approached him inside the makeshift building he had the titan in. How he’d managed to capture it, Levi couldn’t figure out. It was chained up and secured to the ground with lots of pegs. Clearly Stan had  _some_ understanding about how dangerous titans were. That or he was dead-set on it staying put. Levi figured either option was plausible

“Because what you’re doing is wrong, Grunkle Stan!” Mabel said. “This thing shouldn’t be chained up. It could really hurt people if it got loose.”

“Yeah, and so could half of the things at the Mystery Shack. If they were real. But look, this is going to make us a fortune,” Stan argued. 

“Sir, you really shouldn’t have this here. It’s better off dead,” Petra told him. “It could easily kill or maim someone.”

“It’s not going to. I’m going to build a cage around it so it can’t get away,” Stan said. Levi gave him a dark look and drew his blades.

“I’ve had enough of this shit. Get out of the way. I’m taking that thing down,” he growled, moving towards the titan. Stan threw himself in front of it, arms spread out as far as they could go.

“Wait!” he cried. 

“I don’t have time for this,” Levi replied, swinging his blade back. Before he could pull it back down Petra grabbed his arm, forcing him to miss Stan.  _What the fuck does she think she’s doing?!_ Levi hissed at her, giving her a dirty look. She ignored him. 

“We can’t stress enough how bad of an idea this is, but clearly we aren’t going to get through to you,” she said to Stan before turning to Dipper and Mabel. “Be on guard, you two. If something goes wrong find Levi and I, all right?” She pulled on his arm and dragged him out of the enclosure.

“What the fuck was  that?!” he seethed, ripping his arm away from her grasp. “You’re putting those kids and their lackwit of an uncle at risk. If you think for a moment -”

“We weren’t getting through to him, Levi. He was dead set and there was no point of killing him to get to the titan,” Petra replied heatedly.

“I would’ve gotten rid of the problem, wouldn’t I?” he demanded.

“If you killed him then who would take care of Dipper and Mabel? And what would happen to us if someone found out you killed him?” she pointed out. “The consequences would have been bad. What we need to do is go back tonight and kill the titan when no one’s around.” 

“We can’t wait until tonight. That gives the titan too many chances to escape. We need to do this now,” Levi argued.

“Look, I don’t like waiting either,” she said, giving him a stern look. “But there’s nothing we can do. Our best bet is sneaking into the enclosure and kill the titan.”

“But when are we going to get that chance? We can’t do it tonight; it’ll be too dark,” Levi pointed out.

“Perhaps early tomorrow morning?” 

“That’s gives the titan an even larger time frame of escaping.”

“Well, maybe it won’t. Stan seems to have it well restrained. And besides, we should go out and look for some more portals. For now, let’s just assume this one is taken care of. We need to go look for a way home.”

“What’s the point of looking for a portal when it’ll close up in minutes? We need to make sure all of the titans are gone before we leave.”

“Our portal stayed open for weeks. We might find one that’s the same,” Petra said. Part of Levi didn’t want to go look for a portal. He wanted to figure out how to take out the titan and (although he’d never admit it) a small part of him wanted to stay in Gravity Falls. But Petra had a point; they’d be wasting their time trying to kill the titan and they needed to find a way home. 

“Good point. Let’s go,” he said. 

  
  


The forest was alive with noise as Levi and Petra made their way through the trails, eyes peeled for portals. Since they had arrived they hadn’t found any new evidence of more portals popping up and the idea that they may be stuck in this world forever scared and excited Levi.  _We need to go back home,_ he thought as he pushed away from branches and went off-trail.  _We don’t belong here. We don’t have a way to live well here._

“Have you found anything yet?!” Petra yelled from somewhere down the trail.

“No!” he shouted back. “Tch. We’re going to be here all night if we keep this up,” he added as his blue eyes flitted up to the darkening sky. 

“We should go back to the cabin. It’s getting dark,” she said. 

“We still have some daylight left,” he argued.

“But do we want to stumble back in the dark?” He groaned and went back to the trail.

“All right. We’ll call it quits for the day,” he gave in. They started walking back towards the trail that led back to their cabin. Levi was sure it’d be dark by the time they got back anyway, but at least they spent a good few hours looking for a way back home.

“Hey, Levi?” Petra asked, breaking the comfortable silence between the two.

“Yeah? What is it?”

“What are we going to do if we can’t get home?” 

“We’re going to get home eventually. But in the meantime, we -”

“It’s not guaranteed we’ll get home. We don’t know if another portal will show up and it’s possible we won’t even know about it if it does,” she pointed out. “I think we need to have a backup plan in case we have to stay here for much longer. We can’t keep living like this.”

“The hell we can’t. We don’t have any papers, Petra. We can’t live in this world and we don’t belong here. We belong back home and I’ll be damned if I don’t get us there.”

“This isn’t something you can accomplish. We’re completely dependant on some random force of nature. No matter what you do, you can’t make a portal appear and you can’t get us home right now.” 

“What, so you just want us to quit looking?! You want to give up?!”

“No, that’s not what I said. I meant that we need to start making a backup plan. We should still keep looking for a way home but in the meantime we need a plan.”

“I hate it when you’re right,” he groaned. “So what, we find a forger and get some fake papers from him?” 

“I guess. That or we try applying for citizenship, but I don’t think we’d get far,” she said. 

“Forgery is probably our best option. From there, I think we’ll just have to wing it. Find jobs, stay in the cabin until we can legally get a place, and -”

“‘Get a place?’ You want to live together?” Petra asked.  _Shit, did I really say that,_ he thought.

“I just figured it’d be better money-wise for both of us,” he quickly defended himself. 

“Levi, you’re a terrible liar,” she laughed. “I don’t mind living together. I like it, actually.”

“I do too,” he said.  Maybe with a normal life we can forget about the past and move forward. I’d like to go into the future with her.

  
  


The twins were sitting on the couch as Levi and Petra got home. Mabel hopped off as soon as they were in the door, rushing to Levi and grabbing his sweater. 

“Grunkle Stan is unveiling the titan  tonight!” she exclaimed. “We tried talking to him, but he won’t listen to us!”

“What makes you think he’ll listen to us? He already made it clear he doesn’t give a damn about our opinion,” Levi said, grasping Mabel’s hands and gently pulling them off of his sweater. 

“We were thinking maybe we could distract him and you could take care of the titan,” Dipper suggested, joining everyone by the door.

“I don’t think we’re going to be able to kill it tonight, but . . . we might as well go,” Petra shrugged, glancing at Levi. “Who knows what’ll happen. Maybe we’ll get our opportunity.”

“We better. I don’t want this to drag on for much longer,” he said. “We’ll go, but we can’t promise we’ll be able to do anything.”

  
  


Despite the fact Stan seemed like a complete con artist and it would have made sense for no one to trust his crappy promotional flyers, a flock of people showed up at the Mystery Shack, all lined up outside of the small enclosure to see the titan. Dipper and Mabel were collecting money from the prospective customers while Petra and Levi hid in the bushes until Stan moved out of the area.

“Come on, old man. We don’t have all day,” Levi growled, watching as he milled about conning people for more money.  

“Normally I’d say you should be more patient, but I’m ready to go back to the cabin,” Petra sighed. “I really want to take a bath.”

“Once Stan leaves we’ll go in for the kill,” Levi said. 

“That’ll be great once he actually leaves,” she replied, making him snort. 

It all happened in a flash. The sound of clanking metal rose above the din of conversation outside of the enclosure and before Levi and Petra could process what the noise was, the titan, chains still wrapped around its arms and shoulders, stepped out of its makeshift home. 

“Shit!” Petra cried, getting to her feet and running towards the titan, Levi right beside her.  _God damn it, we warned him,_ Levi thought, pushing people out of his way.  _We told him this would happen. If someone dies because of his stupidity . . ._ Thankfully everyone had the sense to run away and the titan was moving slowly. Hopefully it’d be easy to take down. 

“Go somewhere safe,” Petra instructed the twins as they approached her and Levi. 

“But we want to help!” Dipper said. 

“You can’t help with something like this. But here, have these in case something happens and it gets near you. Hold it down here,” Petra instructed, handing them each a blade. The titan smash a window, reaching into the Mystery Shack.  _Shit, someone must have hidden in there,_ Levi thought.

“Petra! Disable it any way you can!” he shouted, eyes searching for any straggling spectators. Dipper was stationed on the porch and Mabel was hiding behind a tree near the forest. Not the best places to hide, but it was better than nothing.

“I’m on it!” She engaged her gear and soared into the sky. Her blades cut into one of the titan’s arms and sent it sprawling back towards the porch. 

“Dipper!” Petra cried, changing course and zooming towards him to get him out of the way. But the building was faster than Petra anticipated and it promptly collapsed over her and Dipper, the titan falling down on top of the overhang. Time seemed to pause for Levi. There was no movement from underneath the broken boards and the thought of Petra dying made every horrible emotion possible bubble up violently in his stomach. 

“Hey, you big dummy! I’m over here!” Mabel screaming brought him out of his reverie. She was yelling at the top of her lungs, waving her blade around wildly and running towards the titan. The titan moved its head and started towards her. 

“Mabel, get away from it!” Levi yelled, springing into actions. He could mourn later. Right now he needed to protect Mabel and everyone else. He anchored his hooks into the titan’s shoulder and he zoomed into the air. But before he could kill it, it grabbed his wires and threw them off, sending Levi flying towards the collapsed porch. Pain shot through his body upon impact, but he tried to ignore it. _Shit, why does she have to be so stubborn,_ he thought as he saw Mabel. She was running towards the titan and Levi’s gear wasn’t moving fast enough. She was right under the titan and she swung her blade, severing its heel in half. “That’s for hurting my brother!” she yelled.  _Good girl._

The titan stumbled and started falling as Levi anchoring his gear into the titan. “Go check on Petra and Dipper!” he commanded her before delivering the fatal blow to the falling titan. Blood spurted from the nape, coating Levi in the disgusting fluids. His handkerchief was out and wiping the blood off of his face as he hurried to help Mabel dig Petra and Dipper out of the debris. Dipper had a deep cut on his forehead and he was coughing. Mabel uncovered Petra, who seemed to have gotten the brunt of the collapse. Her face was cut up and her shoulder looked dislocated, not to mention her clothes were torn and stained with blood. 

“Petra!” he said, sitting in the debris beside her and helping her sit up. 

“I’m fine,” she said weakly and relief immediately flowed through his body. She was alive and that was all that mattered. “Did you get it?”

“Mabel and I killed it,” he informed her. She grinned and gave a small nod. 

“Good.” 

  
  


Thankfully, the Mystery Shack didn’t sustain a lot of damage besides the porch and the broken window. At Mabel and Dipper’s request they came to help rebuild, although they made it clear they were still angry with Stan. Petra handed Levi more nails as he fixed a broken beam on the porch. He’d done this enough in the past, fixing up the old hovel he lived in with Isabel and Farlan. A smirk graced his lips as he remembered scaring Isabel that one night when he fell through the ceiling. It had been unintentional and painful, but the look on her face had been pretty hilarious.

“I need a few more,” he said, reaching down towards Petra. She gave him a few others.

“I never knew you were so handy with this kind of thing,” she said, watching him work. “Maybe we can fix up that cabin once we get the money.”

“Wouldn’t you rather have an apartment?” he asked.

“I would like to be closer to town but if we gave the cabin some TLC it could be really cute. Not to mention we’re already comfy living there,” she pointed out.

“True. How about we keep our options open?” he suggested. She laughed and playfully squeezed his leg.

“That’s what you say about everything,” she said. The porch door opened and Mabel and Dipper walked out.

“Dipper and I made some grilled cheeses!” Mabel announced, raising up her large platter of somewhat burnt food. Levi put the nails and hammer down and climbed down the ladder, more than ready for lunch. Petra and Dipper spread out a large blanket on the grass and got started on eating, not waiting for Stan to join them.

“Have you guys decided what you’re going to do,” Dipper asked. “Are you going to stay here longer or go back?” 

“Well, without another portal, we’re stuck here,” Petra answered. “We’d like to go home but realistically, we can’t.” 

“I know it’s not much, but I could get you some fake papers and fake letters of reference so you can live here and get jobs until you find a way back,” Stan offered and although Levi hated this man, he felt excitement at the prospect at being able to truly live in a world without titans, although part of him felt guilty for not trying harder to return home to the walls.

“You’d do that for us?” Petra asked.

“Think of it as a thank you for protecting the kids and helping us rebuild the Mystery Shack,” he said. 

“Thank you, sir. We really appreciate it,” Petra told him. Her gold eyes glanced over to Levi, a large smile on her lips. He knew she was just as excited as him to be able to start a new life here.


	4. Chapter 4

Ever since it opened a year ago, GraviTea Falls was one of the most popular cafes in the entire county. The name had started off as a joke Dipper made but it stuck and eventually Levi and Petra used it officially to open their small store and cafe a little less than a year ago. It was a busy summer day and with a tour bus coming through it was even busier than usual. By the time closing came around eight o’clock, Levi and Petra were exhausted.

Levi was ready to start locking up when the door opened, the annoying little bell Petra insisted on putting up chiming. _Tch, can’t they tell we’re closed,_ he thought in irritation. He went out into the dining area, ready to break the news, but instead of customers he saw Dipper and Mabel Pines. 

“Petra, get out here. The twins are here to see us,” he called back to her as Mabel nearly knocked him down with a forceful hug. “Hey there, Mabel.” 

“We got your wedding invitation in our mail!” she said excitedly. “Congratulations!” 

“Mabel woke up half of the neighborhood when she got it,” Dipper said with a small grin. 

“And Dipper woke up the other half,” Mabel added. “I can’t believe it’s happening! I’ve been waiting for this for forever!” Levi grinned as Petra joined them in the front of the door, a large smile on her face as well. 

“I know! We’re really excited,” she said, giving the twins a big hug. “You’ll be able to come, right?” 

“Of course! We wouldn’t miss it for the world,” Dipper said. “So, how has the shop been holding up?” 

“Great! We’re getting good business! We think we have enough money to move into that small Victorian a few blocks down from the old, run-down convenience store,” she said. 

“Isn’t that house supposed to be haunted?” Mabel asked. 

“Eh, if it is Levi and I can do an exorcism,” Dipper shrugged. 

“I am _never_ performing an exorcism with you again. Not after the last time,” Levi said bluntly. 

“Hey, I didn’t know it was a demon! I thought it was a poltergeist!” Dipper defended himself. 

“The only reason we got rid of it was because that creepy triangle got to him before we did,” Petra pointed out. Levi rolled his eyes. 

“I’d give anything to forget that whole ordeal,” he said. 

“So, I guess that means you aren’t up for a little paranormal creature hunt tonight?” Dipper asked, temptation in his voice. 

“It depends. Are we going after demons or something harmless?” Levi asked back. 

“Not sure. Mabel and I have been talking to people around town and they’ve been telling us about this weird bird that’s in the forests. No one knows what it is and the reports are spanning all the way back to last summer! If that’s too dangerous for you, I guess me and Mabel can handle it on our own,” Dipper said. 

“It sounds like a fun night out and not too dangerous for us,” Petra grinned, glancing at her fiancé. “Let us lock up and we’ll come with.” 

  
  


The forest was darker than normal. Shadows blacker than the night flitted about and the bloody cries of birds screeched through the air. Petra’s hand squeezed Levi’s every time a cry came out of the darkness. He didn’t feel like she was scared; no, it was more of a surprised reaction than anything. _A year away from the titans and she’s jumpy as hell,_ he thought, suppressing a smirk. _Although if she’s going to be like this, I’d rather have her be it here than inside the walls._

The four carried flashlights and their supplies, swinging beams of light in front of them and into the dark forest when they heard nearby cries. Levi and Petra wore their gear over their homemade sweaters and jeans. It had been so long since Levi had last worn his gear he wasn’t used to the friction against his belts as they brushed against each other while walking. 

“So what exactly are we looking for?” Petra asked. 

“It’s a giant bird,” Dipper began. “According to the people who’ve seen it, it’s white and silver but they don’t know whether it’s dangerous or not. It’s nocturnal, I think, since all of the sightings have been at night.” 

“Who’s seen it?” Levi inquired. 

“Toby, Manly Dan, a few other townspeople whose names I can’t remember.” 

“Are we really going to trust Toby?” Levi asked in disdain; Petra giggled. 

“Toby might be weird, but he’s a good source,” Mabel stood up for him. “Just because he tap dances and wears a glittery unitard doesn’t mean he’s a liar.” 

“If anything, it just means his sense of fashion is horrible,” Petra said snarkily, making Levi chuckle. 

“Now we’re onto something,” Dipper laughed. A loud screech cut through the air. Petra’s hand jerked, crushing Levi’s hand for a second before relaxing. He pointed his flashlight towards the source of the noise. Dipper gasped at the sight of a large white bird; it must have been as large as Levi. 

“Mabel, get the net ready!” Dipper whisper-shouted. She drew it out of her bag and held it up in anticipation. The bird cawed and looked down at the four. Levi’s stomach lurched as it’s eyes faded from black into a bloody red. _That’s not a good sign._

“Mabel, let me do this,” he said, hand reaching out to grab the net from her. 

“No, I got it, Levi,” she whispered back. But before she could make any move to capture the creature it shrieked and dive-bombed the group. Levi pushed Mabel out of the way in time, but the thing soon turned around and went after Petra. _Shit!_ He engaged his gear, drawing his blades. _This thing is dangerous. I need to take it out._ Petra flew out of the bird’s way with a small shout of shock. Its eyes were now tomato red and once again it opened its beak. A blinding ray of light shot out of its mouth and hit the ground. Wind rushed around them and a hole grew in the ground. Oh fuck. 

There was now a portal on the ground. 

Time felt like it stopped. Levi stared at the portal. All along, this weird bird had been causing them. Here was their chance to return home; assuming that’s where the portal led. Levi knew humanity back inside the walls needed him and Petra. There was sure as hell no way they’d finished wiping out all of the titans in a year. But he didn’t want to leave. He’d built a life for himself and for Petra in a world where they didn’t have to worry about food, or land, or titans. He and Petra could return to the walls and the thought made his stomach violently sick. 

The bird swooped towards Petra against and she narrowly missed its attack. It hissed at her and butted its head into her stomach. She stumbled back and to Levi’s horror, fell into the portal. He didn’t have to think. His body flew across the short distance, throwing himself down the portal after her. Multicolored lights flew by him as he tried to make himself fall faster, desperate to reach Petra. 

“Levi!” she screamed, reaching out to him. Their fingers brushed together and Levi forced his shoulder upwards. His fingers grabbed hers and he pulled himself towards her. Fear was painted on her face, eyes becoming glossy with tears. 

“Are you hurt?” he asked. 

“No, I’m fine. I-I, do you think we’re heading back to the walls? Or somewhere else?” she questioned. A wave of nerves-induced nausea hit him like a punch to the gut. 

“I don’t know, but nothing can be worse than the hell around the walls,” he replied. _What if we’re going back? What are we going to do? Everyone in the walls needs us, but what about Dipper and Mabel? They need us too. And Petra and I had our lives set out for us. We can’t just give up our dream._

“Promise me we’ll get married one day!” she cried out suddenly, tears starting to stream down her face. “Promise me that no matter what we’ll always be together!” 

“You have my word, Petra,” he said. He grabbed her shoulder and pulled her into a kiss. Heat flowed through his veins at the familiar touch of her lips but his nerves intensified. Who knew where they were going? This could be the last kiss he’d ever share with her. 

The feeling of falling switched to flying into the void and before they could brace themselves they were thrown out of the portal and into the air. Levi hit compacted dirt with a thud, the wind getting knocked out of his chest. Shit, that hurt. He slowly sat up as the sound of rushing feet grew louder. He and Petra were back in the small fortress built outside of Wall Maria and their comrades were rushing towards them. 

“Oh my God, you’re okay!” Nifa cried, helping Petra to her feet. “We were sure you had died! Thank goodness you and Levi are okay.” 

“You guys are still here?” Petra asked incredulously. 

“Why wouldn’t it be? It’s only been a few hours,” Erwin told her. _A few hours? But we’ve been gone for a year. Does time go faster there,_ Levi wondered. 

“Well? What happened?” Hange asked, excited but concerned as she helped Levi up. “Did you see the other side? What was it like?” The memories flashed before his eyes. Fighting the titan bent on killing the crowd Stan Pines had gathered. Kissing Petra for the first time. Teaching Dipper and Mabel self-defense. Moving into a small apartment with Petra. Opening GraviTea Falls with her. Their first time making love. The night he proposed to her. 

“It wasn’t half bad,” he replied, his voice strained. 

  
  


Months later, Petra walked up the staircase to Levi’s office, a stack of paperwork in her hands. She knew he wasn’t going to like getting all of this, especially considering it was his day off, but Hange had told her this was important and couldn’t wait until tomorrow. _I just hope he’s not too upset,_ Petra thought as she knocked on his door. The engagement ring he’d bought for her a year ago was cool against her chest; the engagement was still on but a secret, and so she wore the ring on a chain tucked underneath her clothing. Having to hide the relationship from disapproving superiors was something they both disliked, but there was no way in hell she’d leave him. Now that she thought about it, he didn’t talk much about their experience in Gravity Falls other than referencing moments they spent with themselves or with the twins, but the latter were occasional and getting less and less talked about. She didn’t blame him. It hurt to talk about the twins, especially since they never got a proper goodbye and with no portal activity (at least, from what they could tell), they would never see Dipper or Mabel again. And they would never get to live the life they’d planned while in Gravity Falls. 

“Name and business?” Levi called out, pulling her out of her reverie. 

“It’s Petra, sir. I have some paperwork from Hange.” 

“Of course,” he sighed in exasperation. “Come in, Petra.” She opened the door and quickly entered his office. She had to choke back lighthearted giggle as she put the huge stack on papers on his desk. He was wearing the sweater Mabel had made for him all those months ago.

**Author's Note:**

> This came out of the Day 3 prompt for Rivetra Week. This will also be a prequel series to another SnK/Gravity Falls crossover series I already have planned, so there will be a few loose ends (they'll get resolved eventually).


End file.
